1. Technical Field
The present invention relates to a pyrroloquinoline quinone tetraalkali salt and a crystal thereof, methods for producing these, and a composition.
2. Background Art
Pyrroloquinoline quinone is represented by the formula (2).

Pyrroloquinoline quinone (hereinafter, also referred to as “PQQ” or “free form”) is known to have a possibility of having a function as a novel vitamin (coenzyme) and the like, and paid attention to as a useful substance for health supplements, cosmetics and the like. PQQ exists in fungi and yeasts of eukaryotes, not limited to bacteria, and carries out an important function as a coenzyme. PQQ further has been found so far to have many physiological activities including cell growth-stimulating action, anticataractous action, liver disease-preventing/treating action, injury-curing action, antiallergic action, reverse transcriptase-inhibiting action and glyoxalase I-inhibiting action-anticancer action.
Monoalkali salts, dialkali salts and trialkali salts in which 1 to 3 alkali metal ions are attached to pyrroloquinoline quinone have so far been known. Although the alkali salts of PQQ so far reported are known to be water-soluble substances, the solubility of the salts are actually low, and the solubility of their free form is even lower. An alkali salt whose structure has so far been determined as a crystal is a disodium salt (Non Patent Literature 1). A crystal polymorph of a disodium salt is similarly known (Patent Literature 1).
Since PQQ has so far been considered to be decomposed by alkalinity, the structure of crystallized substances thereof under the alkali condition has not been studied (Non Patent Literature 2)